Efficient flowering in plants is important, particularly when the intended product is the flower or the seed produced therefrom. One aspect of this is the timing of flowering: advancing or retarding the onset of flowering can be useful to farmers and seed producers. An understanding of the genetic mechanisms which influence flowering therefore provides a means for altering the flowering characteristics of the target plant.
Species for which flowering is important to crop production are numerous—essentially all crops which are grown from seed, with important examples being the cereals, rice and maize being probably the most agronomically important in warmer climatic zones, and wheat, barley, oats and rye in more temperate climates. Other important seed products are oil seed rape and canola, sugar beet, maize, sunflower, soyabean and sorghum. Many crops which are harvested for their roots are, of course, grown annually from seed and the production of seed of any kind is very dependent upon the ability of the plant to flower, to be pollinated and to set seed. In horticulture, control of the timing of flowering is important. Horticultural plants whose flowering may be controlled include lettuce, endive and vegetable brassicas including cabbage, broccoli and cauliflower, and carnations and geraniums.
The so-called GIGANTEA or GI gene of Arabidopsis thaliana has been implicated in the response of that plant to photoperiod. However, the GI gene has not been conclusively identified or isolated to date, and its sequence has not been determined. Conclusive identification, isolation and sequencing of the GI gene would therefore be desirable to allow manipulation of the flowering process.
In addition to being able to manipulate flowering time, an ability to control starch accumulation in plants would also be useful.
Starch is synthesised by all higher plants and accumulates to high levels in most plants. Starch plays a crucial role in plant metabolism. It is synthesised in chloroplasts during photosynthesis and then degraded to supply energy for metabolism during the subsequent dark period. This causes fluctuations in starch levels, with the highest starch levels occurring at the end of the light period.
GI mutations cause starch to accumulate in the leaves GI starch accumulation follows wild type fluctuations, but has been shown to be two to three times higher than wild type plants. This accumulation is restricted to photosynthetically active tissues (Eimert et al. 1995).
Again, identification, isolation and sequencing of the GI gene would be desirable to allow manipulation of the starch accumulation process.
It is therefore the object of this invention to go some distance towards meeting the above desiderata, or at least to provide the public with a useful choice.